1. Field of the Invention
This invention relates to a data storing and outputting apparatus for storing coded data and reading and outputting the stored data and particularly to a data storing and outputting apparatus for storing coded video data or sound data and reading and outputting the stored data.
2. Description of the Prior Art
A data storing and outputting apparatus for storing program information including video data and sound data and then, reading and outputting it as necessary is known.
In this apparatus, to suppress a capacity of a memory and decrease input and output data rates, the video data and the sound data are compression-coded before storing them in the memory because the video data and the sound data have a large amount of data.
In the compression coding, there is a tendency that a quality in decoding and a capability of data processing decrease with an increase in the compression rate.
That is, to increase the compression rate, quantizing is made coarse or a coding block length is made larger by a prediction coding such as the interframe predictive coding. However, if it is required to keep the quality in decoding high or to keep the capability of data processing high, a compression coding having a low compression rate should be performed.
On the other hand, the coding data rate may be limited if the coded data read from a memory is recorded in another storing medium again or is transmitted to a transmission line.
For example, in a transmission line employing the ATM (Asynchronous Transfer Mode), it is difficult keep a transmission line having a high data rate in a high traffic condition, so that the user is forced to use a transmission line having a low data rate.
In the case of the transmission line having a low data rate, it is necessary to output data coded at the data rate corresponding to the data rate of the transmission line.
In the prior art data storing and outputting apparatus, the output data rate is fixed.